Optical waveguides in image sensors

ABSTRACT

An embodiment relates to an image sensor comprising (a) a optical pipe comprising a core and a cladding, and (b) a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding, and methods of fabricating and using the same. The image sensor could further comprise a lens structure or an optical coupler or an optical coupler over the optical pipe, wherein the lens structure or the optical coupler or the optical coupler is operably coupled to the optical pipe.

FIELD OF INVENTION

The embodiments relate to an integrated circuit manufacture, more particularly, to manufacturing more efficient CMOS image sensors.

BACKGROUND

An image sensor has a large number of identical sensor elements (pixels), generally greater than 1 million, in a Cartesian (square) grid. The distance between adjacent pixels is called the pitch (p). The area of a pixel is p². The area of the photosensitive element, i.e., the area of the pixel that is sensitive to light for conversion to an electrical signal, is normally only about 20% to 30% of the surface area of the pixel.

The challenge of a designer is to channel as much of the light impinging on the pixel to the photosensitive element of the pixel. There are a number of factors that diminish the amount of light from reaching the photosensitive element. One factor is the manner in which the image sensor is constructed. A complementary metal oxide semiconductor (CMOS) image sensor is manufactured by a process of etching and depositing a number of layers of oxides of silicon, metal and nitride on top of crystalline silicon. The layers of a typical sensor are listed in Table I and shown in FIG. 1.

TABLE I Typical Layer Description Thickness (μm) 15 OVERCOAT 2.00 14 MICRO LENS 0.773 13 SPACER 1.40 12 COLOR FILTER 1.20 11 PLANARIZATION 1.40 10 PASS3 0.600 9 PASS2 0.150 8 PASS1 1.00 7 IMD5B 0.350 6 METAL3 31.18 5 IMD2B 0.200 4 METAL2 21.18 3 IMD1B 0.200 2 METAL1 1.18 1 ILD 0.750

In Table I, typically the first layer on a silicon substrate is the ILD layer and the topmost layer is the overcoat. In Table I, ILD refers to a inter-level dielectric layer, METAL1, METAL2 and METAL3 refer to different metal layers, IMD1B, IMD2B and IMD5B refer to different inter-metal dielectric layers which are spacer layers, PASS1, PASS2 and PASS3 refer to different passivation layers (typically dielectric layers).

The total thickness of the layers above the silicon substrate of the image sensor is the stack height (s) of the image sensor and is the sum of the thickness of the individual layers. In the example of Table I, the sum of the thickness of the individual layers is about 11.6 micrometers (μm).

The space above the photosensitive element of a pixel must be transparent to light to allow incident light from a full color scene to impinge on the photosensitive element located in the silicon substrate. Consequently, no metal layers are routed across the photosensitive element of a pixel, leaving the layers directly above the photosensitive element clear.

The pixel pitch to stack height ratio (p/s) determines the cone of light (F number) that can be accepted by the pixel and conveyed to the photosensitive element on the silicon. As pixels become smaller and the stack height increases, this number decreases, thereby lowering the efficiency of the pixel.

More importantly, the increased stack height with greater number of metal layers obscure the light from being transmitted through the stack to reach the photosensitive element, in particular of the rays that impinge the sensor element at an angle. One solution is to decrease the stack height by a significant amount (i.e., >2 μm). However, this solution is difficult to achieve in a standard CMOS process.

Another issue, which possibly is the one that most limits the performance of the conventional image sensors, is that less than about one-third of the light impinging on the image sensor is transmitted to the photosensitive element such as a photodiode. In the conventional image sensors, in order to distinguish the three components of light so that the colors from a full color scene can be reproduced, two of the components of light are filtered out for each pixel using a filter. For example, the red pixel has a filter that absorbs green and blue light, only allowing red light to pass to the sensor.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a cross sectional view of a conventional image sensor.

FIG. 2 shows a cross sectional view of an embodiment of an image sensor.

FIG. 3 shows a cross sectional view of another embodiment of an image sensor having a microlens.

FIG. 4 shows a schematic cross section of a compound pixel having two image sensors having for two apertures (d₁ and d₂) with light pipes for directing light of different wavelengths (λ_(B) and λ_(R)).

FIG. 5 shows different schematic cross sectional view showing the construction of an embodiment of an image sensor.

FIG. 6 shows a schematic cross sectional view of an embodiment of a dual photodiode comprising a first photodiode having substantially the same a cross sectional area as of the optical pipe is located beneath the optical pipe and a second photodiode having substantially the same or greater cross sectional areas than that of the aperture in the stack is located under the first photodiode, and wherein the first photodiode and the second photodiode are separated by a physical barrier to prevent cross talk.

FIG. 7 shows a schematic cross sectional view of an embodiment of a light coupler optically coupled to an image sensor.

FIG. 8 shows different schematic cross sectional views showing the construction of an embodiment of a light coupler optically coupled to an image sensor. The top and bottom figures are cross sections of two complementary pixels (2 pipe lights of different diameters) that create color.

FIG. 9 shows a schematic of a top view of a device containing image sensors of the embodiments disclosed herein, each image sensor having two outputs representing the complementary colors.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

This disclosure is drawn, inter alia, to methods, apparatus, systems, and devices related to an image sensor and compound pixels. An embodiment relates to a method for increasing the efficiency of an image sensor. Another embodiment provides a means for eliminating the color filter so that more than only one-third of the impinging light is use to produce an electrical signal. Another embodiment relates to a method for increasing the efficiency of an image sensor by increasing the amount of electromagnetic radiation such as light impinging on the image sensor. An embodiment of the image sensor comprises an optical pipe such as a light pipe to transfer electromagnetic radiation incident on the image sensor to the photosensitive element on or within the substrate of the image sensor. The optical pipe include of a high refraction index core with a lower refraction index cladding. The end of the optical pipe adjacent to the photosensitive element is about the same size as the photosensitive element so that most or all of the electromagnetic radiation in the pipe impinges on the photosensitive element. A coupler that may take the shape of a micro lens efficiently could be located on the optical pipe to collect and guide the electromagnetic radiation into the optical pipe.

Another embodiment relates to use the optical pipe to eliminate pigmented color filters that absorb about ⅔ of the light that impinges on the image sensor. The core and the cladding of the optical pipe could function as waveguides. Waveguides do not absorb light like color filters, but can be designed to selectively transmit selected wavelengths.

A waveguide has a cutoff wavelength that is the lowest frequency that the waveguide can propagate. As a result, a waveguide in the core whose cutoff wavelength is at green will not propagate red light, and a waveguide in the core whose cutoff wavelength is at blue will not propagate red and green light. In one implementation, a blue waveguide and a blue/green waveguide could be embedded within a white waveguide, which could be in the cladding. For example, any blue light could remain in the blue waveguide in a core, any blue or green light could remain in the green/blue waveguide of another core, and the remainder of the light could remain in the white waveguide in one or more the claddings.

An embodiment relates to an image sensor comprising (a) a optical pipe comprising a core and a cladding, and (b) a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding. Preferably, the image sensor comprises no color filter, or optionally it could comprise a color filter. Preferably, the optical pipe is circular, non-circular or conical. Preferably, the core has a core index of refraction (n₁) and the cladding has a cladding index of refraction (n₂), and further wherein n₁ is greater than n₂. Preferably, the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding. Preferably, the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding without a color filter. Preferably, an electromagnetic radiation beam receiving end of the optical pipe comprises a curved surface. Preferably, the core has a greater cross-sectional area at an electromagnetic radiation beam receiving end of the core than that at an electromagnetic radiation beam emitting end of the core. Preferably, the pair of photosensitive elements are located on or within a substrate.

The image sensor could further comprise a lens structure or an optical coupler over the optical pipe, wherein the lens structure or the optical coupler is operably coupled to the optical pipe. Preferably, the core comprises a first waveguide having a cutoff wavelength such that electromagnetic radiation of wavelength greater than the cutoff wavelength leaks out from the core into the cladding. Preferably, the cladding comprises a second waveguide that permits electromagnetic radiation of wavelength of greater than the cutoff wavelength to remains within the cladding and be transmitted to the peripheral photosensitive element. Preferably, a cross-sectional area of the core at an electromagnetic radiation beam emitting end of the core is substantially equal to an area of the central photosensitive element. Preferably, a cross-sectional area of the cladding at an electromagnetic radiation beam emitting end of the cladding is substantially equal to an area of the peripheral photosensitive element.

The image sensor could further comprise a stack surrounding the optical pipe, the stack comprising metallic layers embedded in dielectric layers, wherein the dielectric layers have a lower refractive index than that of the cladding. Preferably, a surface of the stack comprises a reflective surface. Preferably, the image sensor is a complementary metal oxide semiconductor (CMOS) image sensor. Preferably, the optical is could also be used for charge-coupled devices (CCD). Preferably, an amount of an electromagnetic radiation beam impinging on the image sensor is transmitted to the photosensitive element is greater than about a third of the electromagnetic radiation beam impinging on the image sensor. Preferably, the core has a core index of refraction (n₁), the cladding has a cladding index of refraction (n₂), and the stack has a stack refractive index (n₃), and further wherein n₁>n₂>n₃. Preferably, the photosensitive element comprises a photodiode. Preferably, the core is the first waveguide and the cladding is the second waveguide. Preferably, the lens structure or the optical coupler comprises a curved surface and a flat surface such that the lens structure or the optical coupler is shaped as a stationary liquid droplet. Preferably, the lens structure or the optical coupler comprises a first opening and a second opening with the first opening being larger than the second opening, and a connecting surface extending between the first and second openings. Preferably, a diameter of the first opening is substantially the same as a diameter of the cladding and a diameter of the second opening is substantially the same as a diameter of the core. Preferably, the connecting surface is flat or curved. Preferably, the connecting surface comprises a reflective surface.

Another embodiment relates to a compound pixel comprising at least two different image sensors, each image sensor comprising (a) a optical pipe comprising a core and a cladding, and (b) a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding, wherein each of the at least two different image sensors is configured to separate wavelengths of an electromagnetic radiation beam incident on the compound pixel at a cutoff wavelength, and the compound pixel is configured to reconstruct a spectrum of wavelengths of the electromagnetic radiation beam. Preferably, the core comprises a first waveguide having the cutoff wavelength such that electromagnetic radiation of wavelength greater than the cutoff wavelength leaks out from the core into the cladding, further wherein the cutoff wavelength of the core of each of the at least two different image sensors is different such that the at least two different image sensors separate the electromagnetic radiation beam incident on the compound pixel at different cutoff wavelengths. Preferably, the cladding comprises a second waveguide that permits electromagnetic radiation of wavelength of greater than the cutoff wavelength to remains within the cladding and be transmitted to the peripheral photosensitive element. Preferably, a cross-sectional area of the cladding at an electromagnetic radiation beam emitting end of the cladding is substantially equal to an area of the peripheral photosensitive element. The compound pixel could further comprise a stack of metallic and non-metallic layers surrounding the optical pipe of each of the at least two different optical sensors.

Another embodiment relates to a compound pixel comprising at least a first image sensor and a second image sensor, wherein the first image sensor is configured to provide a first separation of an electromagnetic radiation beam incident on the image sensor at a first cutoff wavelength without any color filter, the second image sensor is configured to provide a second separation of the electromagnetic radiation beam incident on the image sensor at a second cutoff wavelength without any color filter, the first cutoff wavelength is different from the second cutoff wavelength, and the compound pixel is configured to reconstruct a spectrum of wavelengths of the electromagnetic radiation beam. Preferably, the first image sensor comprises a first waveguide having the first cutoff wavelength such that electromagnetic radiation of wavelength greater than the first cutoff wavelength leaks out from the first waveguide, wherein the second image sensor comprises a second waveguide having the second cutoff wavelength such that electromagnetic radiation of wavelength greater than the second cutoff wavelength leaks out from the second, further wherein the first cutoff wavelength is different from the second cutoff wavelength. Preferably, the first image sensor further comprises a first white waveguide that permits electromagnetic radiation of wavelength of greater than the first cutoff wavelength to remains within the first white waveguide and the second image sensor further comprises a second white waveguide that permits electromagnetic radiation of wavelength of greater than the second cutoff wavelength to remains within the second white waveguide. Preferably, the first image sensor comprises a first pair of photosensitive elements and the second image sensor comprises a second pair of photosensitive elements. The compound pixel could further comprise a stack of metallic and non-metallic layers in the vicinity of the first and second waveguides. Preferably, the two different image sensors comprise cores of different diameters. Preferably, the first image sensor comprises a core of a different diameter than that of the second image sensor.

Another embodiment relates to a method of manufacturing an image sensor, comprising (a) forming a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, and (b) forming a optical pipe comprising a core and a cladding, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding.

The embodiments relate to a high efficiency image sensor and a method for increasing the efficiency of an image sensor. The efficiency could be increased when more of the light impinging on an image sensor is received by the photosensitive element and converted to an electrical signal.

The method of manufacturing an embodiment of the image sensor (FIG. 2) comprises the formation of an optical pipe using the principles of an optical fiber waveguide. As shown in FIG. 2, an optical pipe comprises a high refraction index core channel (22) that extends from the end of the image sensor receiving incident electromagnetic radiation beam, e.g., overcoat (15), down to the photosensitive element (24) on or within the substrate (20) with a cladding layer (26) of lower refraction index material surrounding the core. In the image sensor of the embodiments disclosed herein, the color filter (12) in FIG. 2 would be optional, and preferably not be included.

Each of the photosensitive elements (photosensors) typically comprises a photodiode, although not limited to only a photodiode. Typically, the photodiode is doped to a concentration from about 1e(E)16 to about 1e(E)18 dopant atoms per cubic centimeter, while using an appropriate dopant.

The layers 1-11 in FIG. 2 illustrate different stacking layers similar to layers 1-11 of FIG. 1. The stacking layers comprise dielectric material-containing and metal-containing layers. The dielectric materials include as but not limited to oxides, nitrides and oxynitrides of silicon having a dielectric constant from about 4 to about 20, measured in vacuum. Also included, and also not limiting, are generally higher dielectric constant gate dielectric materials having a dielectric constant from about 20 to at least about 100. These higher dielectric constant dielectric materials may include, but are not limited to hafnium oxides, hafnium silicates, titanium oxides, barium-strontium titanates (BSTs) and lead-zirconate titanates (PZTs).

The dielectric material-containing layers may be formed using methods appropriate to their materials of composition. Non-limiting examples of methods include thermal or plasma oxidation or nitridation methods, chemical vapor deposition methods (including atomic layer chemical vapor deposition methods) and physical vapor deposition methods.

The metal-containing layers could function as electrodes. Non-limiting examples include certain metals, metal alloys, metal silicides and metal nitrides, as well as doped polysilicon materials (i.e., having a dopant concentration from about 1e18 to about 1e22 dopant atoms per cubic centimeter) and polycide (i.e., doped polysilicon/metal silicide stack) materials. The metal-containing layers may be deposited using any of several methods. Non-limiting examples include chemical vapor deposition methods (also including atomic layer chemical vapor deposition methods) and physical vapor deposition methods. The metal-containing layers could comprise a doped polysilicon material (having a thickness typically in the range 1000 to 1500 Angstrom) from about 1000 to about 1500 angstroms.

The dielectric and metallization stack layer comprises a series of dielectric passivation layers. Also embedded within the stack layer are interconnected metallization layers. Components for the pair of interconnected metallization layers include, but are not limited to contact studs, interconnection layers, interconnection studs.

The individual metallization interconnection studs and metallization interconnection layers that could be used within the interconnected metallization layers may comprise any of several metallization materials that are conventional in the semiconductor fabrication art. Non-limiting examples include certain metals, metal alloys, metal nitrides and metal silicides. Most common are aluminum metallization materials and copper metallization materials, either of which often includes a barrier metallization material, as discussed in greater detail below. Types of metallization materials may differ as a function of size and location within a semiconductor structure. Smaller and lower-lying metallization features typically comprise copper containing conductor materials. Larger and upper-lying metallization features typically comprise aluminum containing conductor materials.

The series of dielectric passivation layers may also comprise any of several dielectric materials that are conventional in the semiconductor fabrication art. Included are generally higher dielectric constant dielectric materials having a dielectric constant from 4 to about 20. Non-limiting examples that are included within this group are oxides, nitrides and oxynitrides of silicon. For example, the series of dielectric layers may also comprise generally lower dielectric constant dielectric materials having a dielectric constant from about 2 to about 4. Included but not limiting within this group are hydrogels, aerogels, silsesquioxane spin-on-glass dielectric materials, fluorinated glass materials and organic polymer materials.

Typically, the dielectric and metallization stack layer comprises interconnected metallization layers and discrete metallization layers comprising at least one of copper metallization materials and aluminum metallization materials. The dielectric and metallization stack layer also comprises dielectric passivation layers that also comprise at least one of the generally lower dielectric constant dielectric materials disclosed above. The dielectric and metallization stack layer could have an overall thickness from about 1 to about 4 microns. It may comprise from about 2 to about 4 discrete horizontal dielectric and metallization component layers within a stack.

The layers of the stack layer could be patterned to form patterned dielectric and metallization stack layer using methods and materials that are conventional in the semiconductor fabrication art, and appropriate to the materials from which are formed the series of dielectric passivation layers. The dielectric and metallization stack layer may not be patterned at a location that includes a metallization feature located completely therein. The dielectric and metallization stack layer may be patterned using wet chemical etch methods, dry plasma etch methods or aggregate methods thereof. Dry plasma etch methods as well as e-beam etching if the dimension needs to be very small, are generally preferred insofar as they provide enhanced sidewall profile control when forming the series of patterned dielectric and metallization stack layer.

The planarizing layer 11 may comprise any of several optically transparent planarizing materials. Non-limiting examples include spin-on-glass planarizing materials and organic polymer planarizing materials. The planarizing layer 11 could extend above the optical pipe such that the planarizing layer 11 would have a thickness sufficient to at least planarize the opening of the optical pipe 22, thus providing a planar surface for fabrication of additional structures within the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 2. The planarizing layer could be patterned to form the patterned planarizing layer.

Optionally, as shown in FIG. 2, there could be a series of color filter layers 12 located upon the patterned planarizing layer 11. The color filter layers are registered with respect to the photosensor regions 24. Color filter layer 12 while present is not registered with respect to any photosensor region. The series of color filter layers, if present, would typically include either the primary colors of red, green and blue, or the complementary colors of yellow, cyan and magenta. The series of color filter layers would typically comprise a series of dyed or pigmented patterned photoresist layers that are intrinsically imaged to form the series of color filter layers. Alternatively, the series of color filter layers may comprise dyed or pigmented organic polymer materials that are otherwise optically transparent, but extrinsically imaged while using an appropriate mask layer. Alternative color filter materials may also be used. The filter could also be filter for a black and white or IR sensors, wherein the filter cuts off visible and pass IR predominantly.

The spacer layer (13) could be one or more layers made of any material that physically, but not optically, separates the stacking layers from the micro lens (14). The spacer layer could be formed of a dielectric spacer material or a laminate of dielectric spacer materials, although spacer layers formed of conductor materials are also known. Oxides, nitrides and oxynitrides of silicon are commonly used as dielectric spacer materials. Oxides, nitrides and oxynitrides of other elements are not excluded. The dielectric spacer materials may be deposited using methods analogous, equivalent or identical to the methods described above. The spacer layer could be formed using a blanket layer deposition and etchback method that provides the spacer layer with the characteristic inward pointed shape.

The micro lens (14) may comprise any of several optically transparent lens materials that are known in the art. The lens layers may comprise any of several optically transparent lens materials that are known in the art. Non-limiting examples include optically transparent inorganic materials, optically transparent organic materials and optically transparent composite materials. Most common are optically transparent organic materials. Typically the lens layers could be formed incident to patterning and reflow of an organic polymer material that has a glass transition temperature lower than the series of color filter layers 12, if present, or the patterned planarizing layer 11.

In the optical pipe 22, the high index material could, for example, be silicon nitride having a refractive index of about 2.0. The lower index cladding layer material could, for example, be a glass, for example a material selected from Table II, having a refractive index about 1.5.

TABLE II Typical Material Index of Refraction Micro Lens (Polymer) 1.583 Spacer 1.512 Color Filter 1.541 Planarization 1.512 PESiN 2.00 PESiO 1.46 SiO 1.46 In Table II, PESiN refers to plasma enhanced SiN and PESiO refers to plasma enhanced SiO.

Preferably, the cross sectional area of the end of the optical pipe adjacent to the photosensitive element is about the same size as the area of the photosensitive element. Otherwise, electromagnetic radiation guided through the optical pipe outside of the photosensitive element could impinge on non-sensitive regions of the substrate, thereby reducing the amount of light converted to an electrical signal and reducing the efficiency of the image sensor.

Optionally, a micro lens could be located on the optical pipe near the incident electromagnetic radiation beam receiving end of the image sensor. The function of the micro lens or in more general terms is to be a coupler, i.e., to couple the incident electromagnetic radiation beam into the optical pipe. If one were to choose a micro lens as the coupler, its distance from the optical pipe would be much shorter than to the photosensitive element, so the constraints on its curvature are much less stringent, thereby making it implementable with existing fabrication technology.

The shape of the optical pipe could be different for different embodiments. In one configuration, the optical pipe could cylindrical, that is, the diameter of the pipe remains the substantially the same throughout the length of the optical pipe. In another configuration, the optical pipe could conical, where the upper diameter of the cross sectional area of the optical pipe could be greater than the lower diameter of the cross sectional area of the optical pipe. The terms “upper” and “lower” refer to the ends of the optical pipe located closer to the incident electromagnetic radiation beam receiving and exiting ends of the image sensor. Other shapes include a stack of conical sections.

Table II lists several different glasses and their refractive indices. These glasses could be used for the manufacture of the optical pipe such that refractive index of the core is higher than that of the cladding. The CMOS image sensors of the embodiments could be fabricated using different transparent glasses having different refractive indices without the use of pigmented color filters. As waveguides of the embodiments do not absorb light like color filters, but may be designed to selectively transmit selected wavelengths, the light transmission efficiency of the optical pipe could be at least 50%, more preferably at least 75%, most preferably at least 99%, i.e., substantially 100%. With the proper arrangement of waveguides in the optical pipe of the embodiments, it is possible to more efficiently transmit the electromagnetic radiation beam incident on the image sensor to the photosensitive element, thereby increasing the sensitivity of the sensor.

In some embodiments, the optical pipe could be circular in or cross section so as to function as a circular waveguide characterized by the following parameters: (1) the core radius (Rc); (2) the core index of refraction (n₁); and (3) the cladding index of refraction (n₂). These parameters could generally determine the wavelength of light that can propagate through the waveguide. A waveguide has a cutoff wavelength, λct. The portion of the incident electromagnetic radiation having wavelengths longer than the cutoff wavelength would not be confined with the core. As a result, an optical pipe that functions as a waveguide whose cutoff wavelength is at green will not propagate red light though the core, and an optical pipe that functions as a waveguide whose cutoff wavelength is at blue will not propagate red and green light through the core.

By nesting optical pipes that function as waveguides and using a micro lens coupler as shown in FIG. 3, an array of image sensors could be configured to obtain complementary colors having wavelengths of electromagnetic radiation separated at a cutoff wavelength in the core and cladding of each optical pipe of every image sensor. The complementary colors are generally two colors when mixed in the proper proportion produce a neutral color (grey, white, or black). This configuration also enables the capture and guiding of most of the electromagnetic radiation incident beam impinging on the micro lens to the photosensitive elements (i.e., photodiodes) located at the lower end of the optical pipe. Two adjacent or substantially adjacent image sensors with different color complementary separation can provide complete information to reconstruct a full color scene according to embodiments described herein. This technology of embodiments disclosed herein can further supplant pigment based color reconstruction for image sensing which suffers from the inefficiency of discarding (through absorption) the non selected color for each pixel.

Each physical pixel of a device containing an image sensor of the embodiments disclosed herein would have two outputs representing the complementary colors, e.g., (cyan, red) designated as output type 1 or (yellow, blue) designated as output type 2. These outputs would be arranged as follows:

$\begin{matrix} 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & \ldots \\ 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & \ldots \\ 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & 1 & 2 & \ldots \\ \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \; \\ \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \ldots & \; \end{matrix}$

Each physical pixel would have complete luminance information obtained by combining its two complementary outputs. As a result, the same image sensor can be used either as a full resolution black and white or full color sensor.

In the embodiments of the image sensors disclosed herein, the full spectrum of wavelengths of the incident electromagnetic radiation beam (e.g., the full color information of the incident light) could be obtained by the appropriate combination of two adjacent pixels either horizontally or vertically as opposed to 4 pixels for the conventional Bayer pattern.

The image sensors of the embodiments disclosed herein would have a three-fold impact on the future of CMOS image sensor technology.

The first impact would be the increase in the F-number, or the light acceptance cone of each pixel, thereby increasing the overall efficiency of the sensor. Also, with the embodiments disclosed herein, the F-number of the sensor would be relatively insensitive to stack height (distance of the surface of the micro lens to the photodiode). Thus, stack eights of 10 microns or greater could be easily accommodated.

The second impact would be the elimination of color filters (unless desired for some other purposes) whose light absorption characteristics reduce the sensitivity of the conventional image sensor by about a factor of three.

The third impact would stem from the fact that advanced CMOS fabrication processes use metals and materials that may compromise the transparency of the electromagnetic radiation beam such as light propagating through all the metal layers stacked on top of the photoelectric element such as a photodiode. An optical pipe of the embodiments disclosed herein would provide a solution to this problem. Also, the system of the embodiments disclosed herein would decouple the light path of the image sensor, i.e., the optical pipe, from impurities that may be introduced during fabrication of patterned stacked layers of the image sensor. The optical pipe itself, however, should be fabricated with low transmission loss materials such as glasses.

Depending on minimum transistor sizes, each pixel containing an image sensor of the embodiments disclosed herein could be as small as 1 micron or less in pitch and yet have sufficient sensitivity. This could open the way for contact imaging of very small structures such as biological systems.

The embodiments, which include a plurality of embodiments of an image sensor, preferably a CMOS image sensor, as well as methods for fabrication thereof, will be described in further detail within the context of the following description. The description is further understood within the context of the drawings described above. The drawings are for illustrative purposes and as such are not necessarily drawn to scale.

FIG. 4 shows a schematic cross section of an embodiment of a compound pixel having two image sensors having two apertures (d₁ and d₂) with light pipes for directing light of different wavelengths (λ_(B) and λ_(R)). Two photodiodes are constructed under each aperture to capture light of wavelength λ_(B) (or λ_(R)) and of the light of wave length λ_(w-B) (or λ_(w-R)). Note that (w) refers to the wavelength of white light. Signals from the 4 photodiodes (located in 2 pixels) are used to construct color.

FIGS. 5(A) to 5(G) show a series of schematic cross-sectional diagrams illustrating the results of progressive stages in fabricating a CMOS image sensor in accordance with an embodiment of the invention. FIG. 5(A) in particular shows a schematic cross-sectional diagram of the CMOS image sensor at an early stage in the fabrication when photodiodes are constructed. The photodiodes are of an area consistent with the area of the light pipes to be fabricated overlying the photodiodes.

FIG. 5(A) shows a semiconductor substrate. The substrate could include a counter-doped well (having a conductivity type different from the semiconductor substrate) is located within the semiconductor substrate (not shown in FIG. 5(A)). A series of isolation regions could also be located within the semiconductor substrate. The semiconductor substrate could comprise a first region R1 that comprises a photoactive region (shown in FIG. 5(A)) and a laterally adjacent second region R2 that comprises a circuitry region (not shown in FIG. 5(A)).

Within the photoactive region R1, the series of isolation regions separates a series of photosensor regions (i.e., the dual photodiodes shown in FIG. 5(A)). Within the circuitry region R2, the series of isolation regions could separate a pair of active regions. The pair of active regions could include a first field effect transistor T1 and a second field effect transistor T2 located and fabricated therein. The field effect transistors T1 and T2 could comprise a pair of CMOS transistors, since transistor T1 could be located and fabricated within the semiconductor substrate and transistor T2 could located and fabricated within the doped well (having different conductivity type than the semiconductor substrate). Finally, there could be a blanket etch stop layer located conformally covering the first region R1 and the second region R2 including the structures that comprise the field effect transistors T1 and T2.

Within both the photoactive region R1 and the circuitry region R2, the series of isolation regions 12 may comprise materials, have dimensions and be formed using methods that are otherwise conventional in the semiconductor fabrication art.

The series of isolation regions may comprise isolation regions including but not limited to local oxidation of silicon (LOCOS) isolation regions, shallow trench isolation regions (i.e., having a depth up to about 5000 angstroms) and deep trench isolation regions (i.e., having a depth up to about 60000 angstroms). Typically, the first embodiment uses shallow trench isolation regions that are located within shallow isolation trenches. The isolation regions (whether located within shallow isolation trenches or deep isolation trenches) may comprise any of several dielectric materials. Typically included are oxides, nitrides and oxynitrides of silicon, as well as laminates thereof and composites thereof. Oxides, nitrides and oxynitrides of other elements are not excluded.

The series of isolation regions could be formed at least in part using a blanket layer deposition and planarizing method. Appropriate blanket layers may be formed using thermal or plasma oxidation or nitridation methods, chemical vapor deposition methods and physical vapor deposition methods. Planarization methods may include, but are not limited to mechanical planarizing methods, and chemical mechanical polish (CMP) planarizing methods. Chemical mechanical polish planarizing methods are most common.

Within the photoactive region R1, each of the series of photosensor regions may comprise photosensors that are otherwise generally conventional in the semiconductor fabrication art. Each of the photosensors typically comprises a photodiode, although the invention is not limited to a photosensor region as only a photodiode. The photodiodes could be doped to a concentration from about 1e(E)16 to about 1e(E)18 dopant atoms per cubic centimeter, while using an appropriate dopant.

Within the circuitry region R2, each of the pair of field effect transistors T1 and T2 could comprise a gate dielectric layer located upon the semiconductor substrate. A gate electrode could be located upon the gate dielectric layer. Spacer layers could be located adjoining the sidewalls of the gate dielectric layer and the gate electrode. Finally, each of the first transistor T1 and the second transistor T2 could comprise a pair of source/drain regions separated by a channel region located beneath the gate electrode.

Each of the foregoing layers and structures that comprise that first transistor T1 and the second transistor T2 may comprise materials and have dimensions that are conventional in the semiconductor fabrication art. Each of the foregoing layers and structures that comprise the first transistor T1 and the second transistor T2 may also be formed using methods that are conventional in the semiconductor fabrication art.

The gate dielectric layers may comprise any of several gate dielectric materials. Included but not limiting are generally lower dielectric constant gate dielectric materials such as but not limited to oxides, nitrides and oxynitrides of silicon having a dielectric constant from about 4 to about 20, measured in vacuum. Also included, and also not limiting, are generally higher dielectric constant gate dielectric materials having a dielectric constant from about 20 to at least about 100. These higher dielectric constant dielectric materials may include, but are not limited to hafnium oxides, hafnium silicates, titanium oxides, barium-strontium titanates (BSTs) and lead-zirconate titanates (PZTs).

The foregoing gate dielectric materials may be formed using methods appropriate to their materials of composition. Non-limiting examples of methods include thermal or plasma oxidation or nitridation methods, chemical vapor deposition methods (including atomic layer chemical vapor deposition methods) and physical vapor deposition methods. Typically, the gate dielectric layers could comprise a thermal silicon oxide gate dielectric material having a thickness from about 20 to about 70 angstroms.

The gate electrodes may similarly also comprise any of several gate electrode conductor materials. Non-limiting examples include certain metals, metal alloys, metal silicides and metal nitrides, as well as doped polysilicon materials (i.e., having a dopant concentration from about 1e18 to about 1e22 dopant atoms per cubic centimeter) and polycide (i.e., doped polysilicon/metal silicide stack) materials. The gate electrode materials may be deposited using any of several methods. Non-limiting examples include chemical vapor deposition methods (also including atomic layer chemical vapor deposition methods) and physical vapor deposition methods. Typically, each of the gate electrodes 18 comprises a doped polysilicon material having a thickness from about 1000 to about 1500 angstroms.

The spacer layers could be typically formed of a dielectric spacer material or a laminate of dielectric spacer materials, although spacer layers formed of conductor materials are also known. Oxides, nitrides and oxynitrides of silicon are commonly used as dielectric spacer materials. Oxides, nitrides and oxynitrides of other elements are not excluded. The dielectric spacer materials may be deposited using methods analogous, equivalent or identical to the methods used for forming the gate dielectric layers. Typically, the spacer layers could be formed using a blanket layer deposition and etchback method that provides the spacer layers with the characteristic inward pointed shape.

The source/drain regions could be formed using a two-step ion implantation method. The source/drain regions could be implanted at a polarity appropriate to a field effect transistor within which they are formed. The two step ion implantation method uses the gate electrode, with and without the spacer layers, as a mask. Typical concentrations of dopants within the source/drain regions could be from about 1c(E)15 to about 1c(E)22 dopant atoms per cubic centimeter.

The blanket etch stop layer may comprise etch stop materials that are conventional in the semiconductor fabrication art. Non-limiting examples also include oxides, nitrides and oxynitrides of silicon. Oxides, nitrides and oxynitrides of other elements are also not excluded. A particular composition of the etch stop layer could be selected in accordance with a composition of materials located and formed thereover. Thus in light of further disclosure below, the blanket etch stop layer could comprise a nitride etch stop material, although the invention is not so limited. The blanket etch stop layer may be formed using any of several methods. Non-limiting examples include chemical vapor deposition or physical vapor deposition methods. Typically, the blanket etch stop layer comprises a silicon nitride material that has a thickness from about 100 to about 300 angstroms.

FIG. 5(B) shows the results of further processing of the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(A). FIG. 5(B) shows dielectric and metal connections stack, patterned and made of materials commonly used in fabricating CMOS sensors.

FIG. 5(B) shows a dielectric and metallization stack layer located upon the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(A). The dielectric and metallization stack layer comprises a series of dielectric passivation layers. Embedded within the series of dielectric passivation layers includes interconnected metallization layers. Components for the interconnected metallization layers include, but are not limited to contact studs CA, first interconnection layers M1, first interconnection studs V1, second interconnection layers M2, second interconnection studs V2, third interconnection layers M3, terminal interconnection studs V3 and terminal metallization layers M4. One interconnected metallization layer could be connected to a source/drain region of transistor T1 and another interconnected metallization layer could be connected to a source/drain region of transistor T2. A pair of first interconnection layers M1, a pair of second interconnection layers M2 and a pair of third interconnection layers M3 is also located remotely within the photosensor region R1, but still embedded within the dielectric and metallization stack layer shown in FIG. 5(B).

The individual metallization interconnection studs and metallization interconnection layers CA, M1, V1, M2, V2, M3, V3 and M4 that could be used within the interconnected metallization layers may comprise any of several metallization materials that are conventional in the semiconductor fabrication art. Non-limiting examples include certain metals, metal alloys, metal nitrides and metal silicides. Most common are aluminum metallization materials and copper metallization materials, either of which often includes a barrier metallization material, as discussed in greater detail below. Types of metallization materials may differ as a function of size and location within a semiconductor structure. Smaller and lower-lying metallization features typically comprise copper containing conductor materials. Larger and upper-lying metallization features typically comprise aluminum containing conductor materials.

The series of dielectric passivation layers the stack may also comprise any of several dielectric materials that are conventional in the semiconductor fabrication art. Included are generally higher dielectric constant dielectric materials having a dielectric constant from 4 to about 20. Non-limiting examples that are included within this group are oxides, nitrides and oxynitrides of silicon. The series of dielectric layers may also comprise generally lower dielectric constant dielectric materials having a dielectric constant from about 2 to about 4. Included but not limiting within this group are hydrogels, aerogels, silsesquioxane spin-on-glass dielectric materials, fluorinated glass materials and organic polymer materials.

The dielectric and metallization stack layer could comprise interconnected metallization layers and discrete metallization layers M1, M2 and M3 comprising at least one of copper metallization materials and aluminum metallization materials. The dielectric and metallization stack layer may also comprise dielectric passivation layers that also comprise at least one of the generally lower dielectric constant dielectric materials disclosed above. The dielectric and metallization stack layer could have an overall thickness from about 1 to about 4 microns (μm). It may typically comprise from about 2 to about 4 discrete horizontal dielectric and metallization component layers within a stack.

FIG. 5(C) shows a schematic cross-sectional diagram illustrating the results of further processing of the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(B).

FIG. 5(C) shows the results of patterning the dielectric and metallization stack layer to form a patterned dielectric and metallization stack layer that comprises a series of patterned dielectric passivation layers. The patterned dielectric and metallization stack layer has a series of apertures A1 and A2 located therein and registered with the series of photosensor regions.

The patterned dielectric and metallization stack layer may be patterned from the dielectric and metallization stack layer while using methods and materials that are conventional in the semiconductor fabrication art, and appropriate to the materials from which are formed the series of dielectric passivation layers. The dielectric and metallization stack layer may be patterned using wet chemical etch methods, dry plasma etch methods or aggregate methods thereof. Dry plasma etch methods are generally preferred insofar as they provide enhanced sidewall profile control when forming the series of patterned dielectric and metallization stack layer. As is illustrated in FIG. 5(C), the dielectric and metallization stack layer could be patterned to form the patterned dielectric and metallization stack layer while using an etch stop layer as a stop layer.

FIG. 5(D) shows the results of further processing of the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(C).

FIG. 5(D) shows the apertures are filled with materials of high light index of refraction (n1). Optionally, in one embodiment, a reflective layer having a reflective surface conformally and contiguously lining each of the apertures A1 and A2, including the bottoms and sidewalls thereof, and also conformally and contiguously covering top surfaces of the patterned dielectric and metallization stack layer could be formed. The reflective layer could also passivate a terminal metal layer M4.

Dielectric materials within the series of patterned dielectric and metallization stack layer typically have dielectric constants from about 1.4 to about 1.6 (e.g., when comprised of silicon oxide). Aperture fill materials of high light refraction (n1) could have a dielectric constant from about 1.6 to about 2.1. A silicon nitride dielectric material typically has a dielectric constant from about 2.0 to about 2.1, and could be used for forming the high light refraction material filling apertures, but the embodiment is not so limited.

FIG. 5(E) shows the results of further processing of the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(D). Specifically, FIG. 5(E) shows the results of patterning the high light refraction material in apertures A1 and A2 such that material is removed to leave a light pipe structure of high light index of refraction (n1). The foregoing patterning may be implemented using methods and materials that are conventional in the art. Non-limiting examples include wet chemical etch methods and materials, dry plasma etch methods and materials, and aggregate methods and materials thereof. Alternate methods are not excluded.

FIG. 5(F) shows the results of further processing of the CMOS image sensor whose schematic cross-sectional diagram is illustrated in FIG. 5(E). Specifically, FIG. 5(F) shows that the volume around the light pipe is filled with material of index of refraction (n2<n1). Optionally, in one embodiment, it is also possible to leave this volume unfilled.

Optionally, in one embodiment, a planarizing layer could be located upon the reflective layer and/or above filled apertures. The planarizing layer may comprise any of several optically transparent planarizing materials. Non-limiting examples include spin-on-glass planarizing materials and organic polymer planarizing materials. The planarizing layer could have a thickness sufficient to at least planarize the series of apertures A1 and A2, thus providing a planar surface for fabrication of additional structures within the CMOS image sensor.

FIG. 5(G) shows the embodiment in which a reflective layer could be deposited on the stack as discussed above such that the sidewalls of the aperture with the reflective layer. The reflective layer can enhance the light collection efficiency of the image sensor.

Optionally, a series of color filter layers could be located upon the patterned on the apertures. The color filter layers would be registered with respect to the photosensor regions. The series of color filter layers could typically include either the primary colors of red, green and blue, or the complementary colors of yellow, cyan and magenta. The series of color filter layers could comprise a series of dyed or pigmented patterned photoresist layers that are intrinsically imaged to form the series of color filter layers. Alternatively, the series of color filter layers may comprise dyed or pigmented organic polymer materials that are otherwise optically transparent, but extrinsically imaged while using an appropriate mask layer. Alternative color filter materials may also be used.

FIG. 6 shows an embodiment of a dual photodiode under each aperture. Preferably, under each aperture there are 2 photodiodes PD_(B) (or PD_(R)) and PD_(W-B) (or PD_(W-R)). Each photodiode captures charge carriers excited by light of different wavelengths: λ_(B) (or λ_(R)) and λ_(w-B) (or λ_(w-R)). The topology of the two photodetectors (photodiodes) is such that the carriers from different regions of the spectrum do not cross talk. This can be accomplished by creating physical barriers such as trenches or by doping to form high resistive areas.

To achieve the good light detection, it is desirable to create a good coupling of light to the photodiode. In one embodiment, this can be achieved by placing a microlens on top of the pixel, or creating a monolithic coupler. No color filter may be used in the embodiments of the image sensor with or without the microlens or optionally, as explained above, color filter could also be used in the embodiments of the sensor with or without the microlens.

The microlens should to be placed at the appropriate height such as the light is preferably focused on top of the light pipe. FIG. 7 shows a schematic of the microlens positioned at the optimum distance (z) by using a polymeric layer of certain thickness as a spacer. Light is then focused on top of the light pipe which then directs it to the photodiode. Microlens in this embodiment could be created using the standard method used for CMOS sensors.

FIG. 8(A) to (C) show a monolithic coupling structure that can be formed by filling the lens material in a deeper etch. FIG. 8(A) shows that the apertures have a deeper etch, and the light pipe does not extend to the top of the structure. FIG. 8(B) shows the area on top of the light pipe is filled with a polymer of the appropriate surface tension and viscosity to form lens in the normal process used to form microlenses. FIG. 8(C)(top) shows a plurality of the monolithic coupling structures and FIG. 8(C)(bottom) shows a plurality of microlenses patterned on a plurality of light pipe apertures.

The microlenses of the embodiments of the image sensor may comprise any of several optically transparent lens materials that are known in the art. Non-limiting examples include optically transparent inorganic materials, optically transparent organic materials and optically transparent composite materials. Most common could be optically transparent organic materials. The microlens layer could be formed incident to patterning and reflow of an organic polymer material that has a glass transition temperature lower than the series of color filter layers (if present) or the patterned planarizing layer (which is generally present in the embodiments of the image sensors).

The recognition of color and luminance by the embodiments of the image sensors could be done by color reconstruction. Each compound pixel has complete luminance information obtained by combining its two complementary outputs. As a result, the same image sensor can be used either as a full resolution black and white or full color sensor.

The color reconstruction could be done to obtain full color information by the appropriate combination of two adjacent pixels, which could be one embodiment of a compound pixel, either horizontally or vertically. The support over which color information is obtained is less than the dimension of two pixels as opposed to 4 for the Bayer pattern.

Each physical pixel of a device containing an image sensor of the embodiments disclosed herein would have two outputs representing the complementary colors, e.g., cyan, red (C, R) designated as output type 1 or yellow, blue (Y, B) designated as output type 2 as shown in FIG. 9. These four outputs of two pixels of a compound pixel can be resolved to reconstruct a full color scene of an image viewed by a device containing the image sensors of the embodiments described herein.

The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of diagrams, flowcharts, and/or examples. Insofar as such diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein can be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system generally includes one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems.

The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures can be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to optical coupling to permit transmission of optical light, for example via an optical pipe or fiber, physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

All references, including but not limited to patents, patent applications, and non-patent literature are hereby incorporated by reference herein in their entirety.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

1. An image sensor comprising (a) a optical pipe comprising a core and a cladding, and (b) a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding.
 2. The image sensor of claim 1, wherein the image sensor comprises no filter.
 3. The image sensor of claim 1, wherein the optical pipe is circular, non-circular or conical.
 4. The image sensor of claim 1, wherein the core has a core index of refraction (n₁), the cladding has a cladding index of refraction (n₂), and the stack has a stack refractive index (n₃), and further wherein n₁>n₂>n₃.
 5. The image sensor of claim 1, wherein the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding.
 6. The image sensor of claim 1, wherein the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding without a filter.
 7. The image sensor of claim 1, wherein an electromagnetic radiation beam receiving end of the optical pipe comprises a curved surface.
 8. The image sensor of claim 1, wherein the core has a greater cross-sectional area at an electromagnetic radiation beam receiving end of the core than that at an electromagnetic radiation beam emitting end of the core.
 9. The image sensor of claim 1, wherein the pair of photosensitive elements are located on or within a substrate.
 10. The image sensor of claim 1, further comprising a lens structure or an optical coupler over the optical pipe, wherein the lens structure or the optical coupler is operably coupled to the optical pipe.
 11. The image sensor of claim 1, wherein the core comprises a first waveguide having a cutoff wavelength such that electromagnetic radiation of wavelength greater than the cutoff wavelength leaks out from the core into the cladding.
 12. The image sensor of claim 11, wherein the cladding comprises a second waveguide that permits electromagnetic radiation of wavelength of greater than the cutoff wavelength to remains within the cladding and be transmitted to the peripheral photosensitive element.
 13. The image sensor of claim 1, wherein a cross-sectional area of the core at an electromagnetic radiation beam emitting end of the core is substantially equal to an area of the central photosensitive element.
 14. The image sensor of claim 1, wherein a cross-sectional area of the cladding at an electromagnetic radiation beam emitting end of the cladding is substantially equal to an area of the peripheral photosensitive element.
 15. The image sensor of claim 1, further comprising a stack surrounding the optical pipe, the stack comprising metallic layers embedded in dielectric layers, wherein the dielectric layers have a lower refractive index than that of the cladding.
 16. The image sensor of claim 15, wherein a surface of the stack comprises a reflective surface.
 17. The image sensor of claim 1, wherein the image sensor is a complementary metal oxide semiconductor (CMOS) image sensor.
 18. The image sensor of claim 1, wherein an amount of an electromagnetic radiation beam impinging on the image sensor is transmitted to the photosensitive element is greater than about a third of the electromagnetic radiation beam impinging on the image sensor.
 19. The image sensor of claim 15, wherein the core has a core index of refraction (n₁), the cladding has a cladding index of refraction (n₂), and the stack has a stack refractive index (n₃), and further wherein n₁>n₂>n₃.
 20. The image sensor of claim 1, wherein the photosensitive element comprises a photodiode.
 21. A compound pixel comprising at least two different image sensors, each image sensor comprising (a) a optical pipe comprising a core and a cladding, and (b) a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding, wherein each of the at least two different image sensors is configured to separate wavelengths of an electromagnetic radiation beam incident on the compound pixel at a cutoff wavelength, and the compound pixel is configured to reconstruct a spectrum of wavelengths of the electromagnetic radiation beam.
 22. The compound pixel of claim 21, wherein the core comprises a first waveguide having the cutoff wavelength such that electromagnetic radiation of wavelength greater than the cutoff wavelength leaks out from the core into the cladding, further wherein the cutoff wavelength of the core of each of the at least two different image sensors is different such that the at least two different image sensors separate the electromagnetic radiation beam incident on the compound pixel at different cutoff wavelengths.
 23. The compound pixel of claim 22, wherein the cladding comprises a second waveguide that permits electromagnetic radiation of wavelength of greater than the cutoff wavelength to remains within the cladding and be transmitted to the peripheral photosensitive element.
 24. The compound pixel of claim 21, wherein a cross-sectional area of the cladding at an electromagnetic radiation beam emitting end of the cladding is substantially equal to an area of the peripheral photosensitive element.
 25. The compound pixel of claim 21, further comprising a stack of metallic and non-metallic layers surrounding the optical pipe of each of the at least two different optical sensors.
 26. A compound pixel comprising at least a first image sensor and a second image sensor, wherein the first image sensor is configured to provide a first separation of an electromagnetic radiation beam incident on the image sensor at a first cutoff wavelength without any filter, the second image sensor is configured to provide a second separation of the electromagnetic radiation beam incident on the image sensor at a second cutoff wavelength without any filter, the first cutoff wavelength is different from the second cutoff wavelength, and the compound pixel is configured to reconstruct a spectrum of wavelengths of the electromagnetic radiation beam.
 27. The compound pixel of claim 26, wherein the first image sensor comprises a first waveguide having the first cutoff wavelength such that electromagnetic radiation of wavelength greater than the first cutoff wavelength will not be confined by the first waveguide, wherein the second image sensor comprises a second waveguide having the second cutoff wavelength such that electromagnetic radiation of wavelength greater than the second cutoff wavelength leaks out from the second, further wherein the first cutoff wavelength is different from the second cutoff wavelength.
 28. The image sensor of claim 27, wherein the first image sensor further comprises a first white waveguide that permits electromagnetic radiation of wavelength of greater than the first cutoff wavelength to remains within the first white waveguide and the second image sensor further comprises a second white waveguide that permits electromagnetic radiation of wavelength of greater than the second cutoff wavelength to remains within the second white waveguide.
 29. The compound pixel of claim 28, wherein the first image sensor comprises a first pair of photosensitive elements and the second image sensor comprises a second pair of photosensitive elements.
 30. The compound pixel of claim 29, further comprising a stack of metallic and non-metallic layers in the vicinity of the first and second waveguides.
 31. A method of manufacturing an image sensor, comprising (a) forming a pair of photosensitive elements comprising a central photosensitive element and a peripheral photosensitive element, and (b) forming a optical pipe comprising a core and a cladding, wherein the central photosensitive element is operably coupled to the core and the peripheral photosensitive element is operably coupled to the cladding.
 32. The method of claim 31, wherein the image sensor comprises no filter.
 33. The method of claim 31, wherein the cross section of the optical pipe is circular, non-circular or conical.
 34. The method of claim 31, wherein the core has a core index of refraction (n₁) and the cladding has a cladding index of refraction (n₂), and further wherein n₁ is greater than n₂.
 35. The method of claim 31, wherein the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding.
 36. The method of claim 31, wherein the optical pipe is configured to separate wavelengths of an electromagnetic radiation beam incident on the image sensor at a cutoff wavelength through the core and the cladding without a filter.
 37. The method of claim 31, wherein an electromagnetic radiation beam receiving end of the optical pipe comprises a curved surface.
 38. The method of claim 31, wherein the core has a greater cross-sectional area at an electromagnetic radiation beam receiving end of the core than that at an electromagnetic radiation beam emitting end of the core.
 39. The method of claim 31, wherein the pair of photosensitive elements are located on or within a substrate.
 40. The method of claim 31, further comprising a lens structure or an optical coupler over the optical pipe, wherein the lens structure or the optical coupler is operably coupled to the optical pipe.
 41. The method of claim 31, wherein the core comprises a first waveguide having a cutoff wavelength such that electromagnetic radiation of wavelength greater than the cutoff wavelength leaks out from the core into the cladding.
 42. The method of claim 41, wherein the cladding comprises a second waveguide that permits electromagnetic radiation of wavelength of greater than the cutoff wavelength to remains within the cladding and be transmitted to the peripheral photosensitive element.
 43. The method of claim 31, wherein a cross-sectional area of the core at an electromagnetic radiation beam emitting end of the core is substantially equal to an area of the central photosensitive element.
 44. The method of claim 31, wherein a cross-sectional area of the cladding at an electromagnetic radiation beam emitting end of the cladding is substantially equal to an area of the peripheral photosensitive element.
 45. The method of claim 31, further comprising a stack of metallic and non-metallic layers surrounding the optical pipe.
 46. The method of claim 31, further comprising a filter.
 47. The method of claim 31, wherein the image sensor is a complementary metal oxide semiconductor (CMOS) image sensor or charge-coupled device (CCD).
 48. The method of claim 31, wherein at least one half amount of an electromagnetic radiation beam impinging on the image sensor is transmitted to the photosensitive element.
 49. The method of claim 31, wherein the core comprises a SiN-containing material and the cladding comprises glass.
 50. The method of claim 31, wherein the photosensitive element comprises a photodiode.
 51. The image sensor of claim 1, further comprising a filter.
 52. The image sensor of claim 12, wherein the core is the first waveguide and the cladding is the second waveguide.
 53. The image sensor of claim 10, wherein the lens structure or the optical coupler comprises a curved surface and a flat surface such that the lens structure or the optical coupler is shaped as a stationary liquid droplet.
 54. The image sensor of claim 10, wherein the lens structure or the optical coupler comprises a first opening and a second opening with the first opening being larger than the second opening, and a connecting surface extending between the first and second openings.
 55. The image sensor of claim 54, wherein a diameter of the first opening is substantially the same as a diameter of the cladding and a diameter of the second opening is substantially the same as a diameter of the core.
 56. The image sensor of claim 54, wherein the connecting surface is flat or curved.
 57. The image sensor of claim 54, wherein the connecting surface comprises a reflective surface.
 58. The compound pixel of claim 21, wherein the two different image sensors comprise cores of different diameters.
 59. The compound pixel of claim 21, wherein the spectrum of wavelengths comprises wavelengths of visible light.
 60. The compound pixel of claim 26, wherein the first image sensor comprises a core of a different diameter than that of the second image sensor and the spectrum of wavelengths comprises wavelengths of visible light.
 61. The compound pixel of claim 21, wherein a plurality of pixels are arranged on a square lattice, an hexagonal lattice, or in a different lattice arrangement. 